Composition for acoustical devices



COATING OR PLASTIC.

UNITED STATES Exa EARL EHRHARDT, OF CHICAGO, ILLINOIS COMPOSITION FOR ACOUSTIGAL DEVICES No Drawing. Application flled May 18,

' .rector or other like and similar objects,

whereby the rendition of sound will be so true and faithful to the original natural sound that distinction between the two cannot be detected.

In acoustical devices, such as sound horns, reproducers, air column speakers, and even those of the hardened plastic type, there is generally the disadvantage of absorption of certain parts of the sound, such as the harmonics, thus leaving the fundamental only to pass with a resultant unnatural rendition. Usually also, the emitted sound proceeds with a hollow or cistern noise or sound; in some cases the sound is mufiled; in some there is a resonance pecu liar to the material used in the device, which resonance or foreign vibrations are parasitic to the sound reproduced, hence effecting again an unnatural and false result; and in some the sound seems to proceed from a hard surface and is often termed as a hard sound. In all such cases the reproduced sound is not pleasant; is far from being like the original sound being reproduced.

It is therefore an object of the invention to produce a sound device of a composition or material having the properties and characteristics to avoid and eliminate all of the disadvantages mentioned, such that the device will be inert or dead so that sound cannot be transmitted therethrough nor absorbed thereby; nor dissipated in vibrating the material or resonating the same.

Another object is to provide a sound conducting, directing, reflecting or like surface which is preferably sufliciently rough, as by the presence of granular particles, such as sand and the like, for efficiently acting on the sound to prevent any loss of harmonics 1928. Serial N0. 278,922.

or other qualities incident to the original sound being reproduced.

The compositionalso has the advantage of bemg fireproof, controllablein setting so that it may become hard and fully set in a few minutes or in a longer period, such as PATENT OFFICE- an hour or so as'desired. It lends itself for 7 use in trowelling, .flow moulding, hand moulding and other like 0 erations, whether for making the new ob ect, patching or plastering on a form, or the like. It is of such density and weight as not to absorb vibra tlons or to take up. any vibration, andhence has no natural frequency of its own, but is absolutely dead or inert. It makes a strong, rigld and staunch article.

In the preferred illustrative use, it is applied to air column horns or loud speakers of the exponential form, yetis adapted for sound devices, conduits and other like and s1m1lar sound or acoustical constructions.

The composition is preferably composed of prepared plaster, cement and plaster of lfaris, wlth the addition of water or the hke for making a plastic material which will harden into, the form given it. The prepared, plaster usually comprises, plaster of flai 1 s sand or other like binding mattha'lfa "g E ezanq l, a preparedpla'ster'having a com posltiora ct f 33? of laster of Paris 33% of screene orpe osanil IQ; of a retarder and about one pound of hair permy be used to give good resu Such a prepared plaster is prepared and sold by the U. S. Gypsum Company, of Chicago, Illinois, under the trade name Big 4. The cement may be that such as known as Portland 0 ment or the equivalent. Plaster of Paris is added to act as a filler or consolidator, inasmuch as prepared plaster is more or less porous and by using a separate quantity of plaster of Paris, the composition as a whole, may be made more solid, compact or consolidated, or more dense. Other material may be used in place of plaster of Paris, such as water putty, and other like and similar materials having the same characteristics as plaster of Paris, for the purpose above mentioned. The ceand a small amount of As an" ment is useful in aiding the hardening and setting of the composition. The ingredients may be mixed in the proportions of about froifn 4;!) to 45% re ared 5 1 50 to 6020 o cement an of lasier of ans and in s'ome cases from 5 to 70. may be added in any desired amofifft, w 1101 may be from 20 to 30 of the composition, but this watei wl l, in the L final composition, be substantially evaporati ed or dissipated, so that there is very little water included in the hardened product.

I In a specific illustrative composition, the

parts Iare milxged fin the PEOPOItiOIlS off six arts weig t o cement our parts 0 reared laster and one part of laster of Paris.

filach of tliese may be varie as eslre suflicient amount of water is added to make the mixture plastic and control the time of l '20 setting. The proportions of the ingredients,

' p when varied, will also vary the time of set-- ting and hardening.

If the prepared plaster does not have a sufficient amount of sand for the purpose of this invention sand may also be added in suflicient prdpbfii'dn to provide the desired roughened or granular surface whereby the 5 sound will be ioperlygnidfifdirected or reflected. By using the sand, a hard substance is formed in the surface, which will not absorb the sound qualities or harmonics, but which will bring out the fine qualities, while at the same time amplifying the sound, thus giving the naturalness to the reproduction and a F as faithful rendition of the original sound. By giving the surface a granular form, reflection of the smaller harmonics is made possible, whereas if a smooth or polis ed surfacekwere used, only the fundamental sound would be 40 reflected from such surface. a e

Cement aids in hardening the'materi'al so that it will be inert or deadand non-resonant.

The invention comprehends other characteristics, as will later appear and are inherently possesesd thereby, and while I have herein disclosed an illustrative embodiment of the invention, it is to be understood that the latter is not limited thereto but may comprehend other features, ingredients, and the like without departing from the spirit there- 0 Having thus disclosed the invention, I claim:

A composition for acoustical devices comprising hardened plastic material containing grains of sand to render the surface rough.

In witness whereof, I hereunto subscribe my name to this specification.

EARL EHRHARDT.

CERTlFlCATE 0F CORRECTION.

Patent Ne. 1,905,631. April 25, 1933.

EARL EHRHARDT.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 81, for "33%" second occurrence, read "66%; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of September, A. D. 1933.

F. M. Hopkins (Seal) Acting Commissioner of Patents. 

